In the production of stained-glass ornamental articles it is common practice to cut pieces of the pattern to be assembled from variously colored glass sheets or panes and to assemble the pieces in a predetermined orientation and pattern. Along the edges of each piece, the adhesive-backed copper foil is applied so that the foil overlaps the faces of the article. It is then common practice to burnish, or smooth down, the copper foil with a fid, roller device, hand pressure or other means. This burnishing is done to ensure good adhesion of the foil tape to the piece's faces and edges, to smooth irregularities such as bunching of the foil at corners and on the faces of convex curves, and therefore, to provide a smooth surface on the faces of the glass pieces for subsequent soldering.
As anyone who has ever applied such copper foil to the edges of glass can testify, it is particularly difficult to apply the foil uniformly such that the amount overhanging the edges, and thus forming the faces, is uniform. For example, a common width of foil used to edge the typical ⅛″ stained glass is 7/32″. If perfectly applied to the edge of the glass, this will provide only a 3/64″ overhang of the foil on each side of the edge for forming on the face of the piece.